A display apparatus has a problem of impaired visibility due to higher luminance of external light than luminance of the display apparatus at the time of being used for digital signage, or electronic signage that is placed outdoors, for example. Further, the luminance of the display apparatus is increased for prevention of an effect of external light, which results in increase of consumption power and costs, thus posing a problem. In order to solve these problems, a semi-transmissive liquid crystal display apparatus has been proposed.
The semi-transmissive liquid crystal display apparatus is a liquid crystal display apparatus which is a hybrid type of a transmissive liquid crystal display apparatus of a backlight-type or the like and a reflective liquid crystal display apparatus. The semi-transmissive liquid crystal display apparatus switches between modes so that in the daytime, reflection of external light such as sunlight is used to produce color, and in cloudy weather or at night, color is produced with use of transmission of backlight.
Video image contents such as static images and moving images are usually created by being targeted at a transmissive liquid crystal display apparatus. Therefore, a semi-transmissive liquid crystal display apparatus having a half mirror or a reflective liquid crystal display apparatus is affected by external light so that color gamut or white balance fluctuate, resulting in display of a video image content in color different from what is intended by a content creator, in some cases.
FIG. 18 is a view showing xy chromaticity 61 at the time of occurrence of color shift due to an effect of external light. The xy chromaticity 61 is xy chromaticity in XYZ colorimetric system which is specified by CIE (Commission Internationale de l'Eclairage), and y chromaticity of the xy chromaticity is on the ordinate and x chromaticity of the xy chromaticity is on the abscissa. Color gamut 605 is color gamut of a color-matching function according to CIE1931. Color gamut 611 is color gamut in producing color with external light, and color gamut 602 is color gamut in producing color with a backlight. The color gamut 611 is shifted with respect to the color gamut 602, and shows that there occurs color shift. Furthermore, white point 613 with external light is shifted from white point 604 with a backlight. That is, color produced at the time of the backlight transmission is different from color produced at the time of the external light reflection.
It has been known that the semi-transmissive liquid crystal display apparatus using a half mirror has an external light reflectivity of several percent with respect to external light luminance of several tens of thousands (cd/m2), for example. This is ascribed to that in a process of reflecting external light with a half mirror, the light needs to pass through a protective glass in the front, a polarizing plate, a liquid crystal display (hereinafter, referred to as “LCD”) panel, a color filter and the like, so that light attenuates due to absorption and diffusion. That is, in the semi-transmissive liquid crystal display apparatus using a half mirror, the reflective rate of external light is low, which results in low luminance generation efficiency.
Additionally, in a display apparatus that is placed outdoors, when a screen size is increased such that the screen size exceeds 100 inches, a part of an area on a screen is illuminated with external light so as to be brighter than the other areas, in some cases. That is, different external light conditions for screen areas may cause luminance and chromaticity for the respective areas to be different.
As a first conventional art, there is an environment-responsive image display system described in Patent Literature 1. The environment-responsive image display system corrects a profile for input and output of a projector based on colored light information of an image display area measured by a colored light sensor. Specifically, coordinate values serving as a complementary pair are operated with a coordinate value in color space under a reference environment which is obtained based on the colored light information in the previous processing and a coordinate value under an actual visual environment, and the profile for input and output is corrected with the coordinate values serving as a complementary pair. The coordinate values serving as a complementary pair are obtained by calculating an inverse vector of a fixed vector showing a coordinate position of a white color value under an actual presentation environment in color space.
As a second conventional art, there is an image observation apparatus described in Patent Literature 2. The image observation apparatus is capable of switching between a reflective type and a transmissive type. When the reflective type is selected, color correction of a display image is performed based on external light information such as a color temperature of external light obtained by an external sensor and information added to image data to be displayed.
As a third conventional art, there is a mobile data processing apparatus described in Patent Literature 3. The mobile data processing apparatus is one using a semi-transmissive liquid crystal display device and controls luminance of a liquid crystal illumination part for causing data to be displayed on a liquid crystal display part with light caused by irradiation from backward of the semi-transmissive liquid crystal display device according to a measured result of a sensor for measuring external luminous energy incident upon the semi-transmissive liquid crystal display device.
As a fourth conventional art, there is a liquid crystal display control apparatus described in Patent Literature 4. The liquid crystal display control apparatus adjusts backlight luminance based on illuminance data from a illumination detection part for detecting luminous energy of external light irradiating a liquid crystal display part from outside, and adjusts a contrast based on the illuminance data from a illumination detection part and temperature data from a temperature detection part for detecting a temperature of the liquid crystal display part.
As a fifth conventional art, there is a display apparatus described in Patent Literature 5. The display apparatus is a semi-transmissive liquid crystal display apparatus for controlling emission intensity of illuminating means of a display panel according to output of an optical sensor disposed at the periphery of a display area, and has spectral sensitivity adjustment means for matching spectral sensitivity of the optical sensor with a visibility characteristic of human.